• 전기학회논문지
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• 제57권8호
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• pp.1377-1382
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• 2008

DSTATCOM(distribution static compensator) is one of the custom power devices, and protects a distribution line from unbalanced and harmonic current caused by non-linear and unbalanced loads. Researches about DSTATCOM are mainly divided two parts, one is the calculation of compensation current and the other part is the current control. Conventional researches use a LPF(low pass filter) to eliminate ripple component at the calculation of compensation current. But this method has a problem that LPF's characteristics restrict the compensation performance of instantaneous active and reactive power. This paper proposes a calculation of compensation current using state observer that can be a counterproposal of conventional methods using LPF. Improved performance of instantaneous active and reactive power compensation was shown by experiments.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 전력전자학술대회 논문집
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• pp.213-214
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• 2014

This paper compares two instantaneous reactive power definitions in DFIG wind turbine with a back-to-back three-level neutral-point clamped voltage source converter under unbalanced grid conditions. In general, conventional definition of instantaneous reactive power is obtained by taking an imaginary component of complex power. The other definition of instantaneous reactive power can be developed based on a set of voltages lagging the grid input voltages by 90 degree. A complex quantity referred as a quadrature complex power is defined. Proposed definition of instantaneous reactive power is derived by taking a real component of quadrature complex power. The characteristics of two instantaneous reactive power definitions are compared using the ripple-free stator active power control algorithm in DFIG. Instantaneous reactive power definition based on quadrature complex power has a simpler current reference calculation control block. Ripple of instantaneous active and reactive power has the same magnitude unlike in conventional definition under grid unbalance. Comparison results of two instantaneous reactive power definitions are verified through simulation.

• 대한기계학회논문집
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• 제18권4호
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• pp.1057-1063
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• 1994

An instantaneous frequency analysis is a technique to examine a signature for the rotating machinery if the signal has several transitions within a cycle. This paper discusses the conditions of existing negative frequency components in the instantaneous frequency. By using a signal consisted of two frequency components, the instantaneous frequency analysis is conducted while the amplitude ratio between two frequency components has been changed. The analysis shows that, depending on the amplitude ratio, the instantaneous frequencies have averaged, zero-valued, or negative components. It turns out that the negative-valued instantaneous frequencies, which have been regarded as the noise effect, are the consequence of the calculation process for the multisignal components. The criteria of existing the negative values in instantaneous frequencies is given in terms of the relative amplitude ratio and the frequency difference. Especially when the amplitude ratio approaches to 1, the instantaneous frequency fluctuates ${\pm}\infty$ in theory, which implies that instantaneous frequency has unstable region around the amplitude ratio, 1.Also, as the frequency difference between major signal components is increased, the region of existing negative instantaneous becomes broader. In an instantaneous frequency analysis, therefore, a narrow band analysis is suggested, with extreme care if the amplitude ratio approaches to 1. In this paper, a vibration signal monitored from a rotating machinery is also examined as an application example in order to show the existence of negative instantaneous frequencies components.

• 대한전기학회논문지:전력기술부문A
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• 제55권12호
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• pp.544-548
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• 2006

The instantaneous frequency gives a frequency value at a time instance. Thus, it is natural to use the instantaneous frequency for detecting disturbances of voltage signal in power line. Various instantaneous frequency estimators are introduced. By applying to different types of disturbed signals, we show the estimators' ability to classify flickers. Also, the computational costs are compared between different instantaneous frequency estimators. The Prony's method (PRONY) and the modified covariance method (MCOV) need relatively smaller amount of calculation than the Teaser-Kaiser energy operator based estimator (DESA II). For an AM-FM modulated signal, the tracking performance of different instantaneous frequency estimators is also compared. Through simulation, it is shown that MCOV produces less variant frequency estimation values than DESA II and PRONY method.

• 전력전자학회논문지
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• 제8권6호
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• pp.576-584
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• 2003

본 논문에서는 비 선형 단상부하에 의해 발생하는 전류 고조파를 보상하기 위한 단상능동전력필터의 새로운 제어방법을 제안한다. 부하전류에 시간지연을 주어 임의의 두 번째 상을 생성한 후 단상시스템을 두 상을 갖는 시스템으로 만들어 복소계산을 가능하게 한다. 기존의 방법은 부하전류를 1/4 T(T는 기본파의 주기) 만큼 지연시켜서 가상의 상을 만들었지만, 본 논문에서 제안하는 방법은 저역통과필터가 상 지연의 특성을 가지는 것을 이용하여 필터를 통과한 지연된 위상을 가진 새로운 신호를 두 번째 상으로 이용하였다. 두 개의 위상이 다른 상이 존재하므로 고조파 전류의 순시계산이 가능하게 된다. 기존의 고정좌표계를 이용하여 순시무효전력이론을 적용하지 않고, 본문에서는 전원주파수에 동기하는 회전좌표계를 사용하여 순시계산을 하였고, 보상전류 지령치를 구하였다. 전류원으로 사용되는 RL부하에 대하여 시뮬레이션과 실험을 수행하였고, 제안된 제어법의 유효성을 입증하였다.

• Journal of Electrical Engineering and Technology
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• 제3권1호
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• pp.94-100
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• 2008

This paper presents a new control method of single-phase active power filter (APF) for the compensation of harmonic current components in nonlinear loads. To facilitate the possibility of complex calculation for harmonic current detection of the single phase, a single-phase system that has two phases was constructed by including an imaginary second-phase giving time delay to the load current. The imaginary phase, which lagged the load current T/4 (Here T is the fundamental cycle) is used in the conventional method. But in this proposed method, the new signal as the second phase is delayed by the filter. Because this control method is applied to a single-phase system, an instantaneous calculation was developed by using the rotating reference frames synchronized to source-frequency rather than by applying instantaneous reactive power theory that uses the conventional fixed reference frames. The control scheme of single-phase APF for the current source with R-L loads is applied to a laboratory prototype to verify the proposed control method.

• 전기학회논문지P
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• 제66권1호
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• pp.1-6
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• 2017

Recently, many motor analysis methods have been developed and studied. Among these methods, the finite element method(FEM) and the analytic method are most popular in field engineers because of the accuracy of FEM and the convenience and rapid analysis time of the analytic method. Contrary, the finite element method has a weakness in calculation time and it is not easy to obtain the instantaneous characteristics value of motor with the analytic method. In this paper, the authors proposes a novel method for calculating the instantaneous characteristics of motors with the magnetic slot equivalent circuit.

• 오토저널
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• 제12권4호
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• pp.35-46
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• 1990

The instantaneous friction in main bearings of a single cylinder diesel engine was determined by measuring the instantaneous angular velocity, calculating the resulting forces acting on the bearings, and solving the unsteady Reynolds equation in combination with the mobility method. The considered system consists of only the crankshaft with flywheel and oil pump. The thermal effects were not considered because of the short testing time. The tests were conducted using an electric start motor. The results indicated that when the bearing is not near equilibrium for very small speeds, simple film lubrication theories are not accurate. The details of grooves and unsteady terms in the Reynolds equation cannot be ignored for increasing efficiency of instantaneous friction calculation of the engine bearings. The effects of speed on instantaneous friction and energy lost in friction were determined.

• Journal of Power Electronics
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• 제9권5호
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• pp.718-725
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• 2009

To get instantaneous reference data in a single power system with vector space phasors, the instantaneous load current is adopted as a phase and another new signal, which is delayed through filtering by the phase-delay property of a low-pass filter, is used as the secondary phase. Because the two-phases have a different phase, the instantaneous value of the harmonic current can be obtained without a time-delay in calculation. The reference voltage is created by multiplying the coefficient k by the compensation current using the rotating reference frame synchronized with the source-frequency. To verify the validity of the proposed control method, experiments are carried out on a prototype of the single-phase hybrid active power filter system.

• 한국자동차공학회논문집
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• 제6권6호
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• pp.267-275
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• 1998

In this study, the instantaneous heat flux measurement probe and the linkage system for the measurement of the instantaneous temperature and heat flux of the DI mono cylinder diesel engine were developed, and these were proved to have a good reliability and sensibility. A 3-D FEM model which consist of full piston to accommodate the eccentric bowl in the piston head, was applied for the analysis of the thermal stress and the temperature distribution. The mean heat flux on the piston head was used as boundary condition for the analysis of piston. The analysis showed that thermal stress concentrate on the bowl and inner surface of pin hall.